Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/40—Picture signal circuits
  • H04N1/40025—Circuits exciting or modulating particular heads for reproducing continuous tone value scales
  • H04N1/40031—Circuits exciting or modulating particular heads for reproducing continuous tone value scales for a plurality of reproducing elements simultaneously
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/40—Picture signal circuits
  • H04N1/40025—Circuits exciting or modulating particular heads for reproducing continuous tone value scales
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/40—Picture signal circuits
  • H04N1/405—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
  • H04N1/4055—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a clustered dots or a size modulated halftone pattern
  • H04N1/4056—Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels producing a clustered dots or a size modulated halftone pattern the pattern varying in one dimension only, e.g. dash length, pulse width modulation [PWM]

Definitions

• Electrographic printing or copying devices are known (for example EP 0 683 954 B1).
• a printing device contains a driven intermediate carrier, for example a photoconductor drum, on which charge images of the images to be printed are generated, which are inked with toner, then re-printed onto a recording medium, for example paper, and fixed there.
• the printing device contains the following components grouped around the intermediate carrier: an exposure device (character generator), a developer station, a transfer printing station, a cleaning station and a loading device.
• the intermediate carrier is charged, for example, to 500 V and then discharged with the exposure device to, for example, approximately 70 V to generate the charge images of the images to be printed.
• the charge images are then colored in the developer station in the usual way with toner.
• the transition from toner to the intermediate carrier only takes place if there is sufficient tension between the developer station, for example a developer roller, and the unloaded areas of the intermediate carrier. If, for example, the developer roller has a potential of 220 V and the charge images on the intermediate carrier are approximately 70 V, a field results which pulls the toner from the developer station onto the intermediate carrier.
• the potential that must be at least fallen below by the discharge of the intermediate carrier in order to enable the intermediate carrier to be colored, is referred to below as the development threshold or development level.
• the toner images are then transferred to the recording medium in the transfer printing station. Finally, the intermediate carrier is cleaned of residual toner in the cleaning station. A new printing process can then begin.
• LEDs light-emitting diodes
• These are usually arranged in a comb of LEDs lying next to one another, which is transverse to the direction of movement of the intermediate carrier.
• the image to be printed is divided into rows and columns of raster cells (macropixels), the raster cells being further divided into output pixels (micropixels) and an LED being assigned to each output pixel.
• micropixels output pixels
• individual output pixels of the grid cell can be exposed accordingly.
• the LEDs can be used in multilevel operation, ie the light energy emitted can be changed by varying the switch-on time and / or the excitation current of the LEDs.
• a realization of such a multilevel operation is described in EP 0 683 954 B1 cited above.
• EP 0 663 760 AI also describes a digital LED printer with an LED comb, in which printed images of different gray values are generated by modulating the exposure time of the LEDs.
• Gray value of a raster cell of the printed image is set over the duration of the light pulse of the LED assigned to the raster cell.
• US 5 255 013 finally describes an LED print head which provides one LED from a comb of LEDs per raster cell (pixel) and in which the gray value of the image to be printed, divided into raster cells, per raster cell by a series of rapidly successive light pulses of the assigned neten LED is generated.
• the problem to be solved by the invention consists in specifying a further method with which a multilevel operation of an exposure device (a character generator) made of LEDs in an electrographic printing or copying device is made possible and a uniform print image is thereby achieved.
• the adjustment of the grayscale levels of the raster cells is thus achieved in the method according to the invention in that the number of light pulses which successively impinge on the intermediate carrier is varied accordingly.
• the control if grid cells are built up, it is advantageous for the control if the light pulses emitted by the LEDs are arranged in groups in the column direction and follow one another directly in the group.
• the light pulses of a group can only ever occur in connection with 100% exposure of a grid cell. It is then sufficient if an LED is provided per raster cell of a row of raster cells, which is controlled in such a way that it emits a corresponding number of successive light pulses during a row period of the raster cells depending on the gray value to be generated, a gray value (not white ) is generated when the discharge of the intermediate carrier caused by the light pulses crosses a development threshold.
• line frequency l / (l [line] x printing speed [m / sec] x39, 37 [inch / m] xresolution [lines / inch]).
• the discharge curve caused by the light pulses on the intermediate carrier always has the same slope, whereby the flank of the discharge curve shifts laterally when additional light pulses are attached, but there are no indentations in the discharge curve.
• the result is that the printed image is uniform and has no irregularities due to undesired crossing of the development threshold in the opposite direction.
• the discharge curve is independent of the printing speed, as long as the length of the light pulse is shorter than the associated time window: e.g. 8 (duration of the light pulse) ⁇ line period of the grid cells, provided that a maximum of eight light pulses are possible per grid cell.
• the discharge curve is largely independent of the shape of the light field of the LED as long as the transmitted energy per LED is identical.
• the discharge curve is monotonically rising / falling between 0 and 100%.
• the energy per light pulse is chosen to be the same and the luminous point generated on the intermediate carrier by the light pulse can be selected to be larger than the grid cell.
• the LEDs are expediently arranged side by side in a comb, one LED per grid cell in the row direction. In order to reduce the current increase when the comb is fully actuated, it is expedient to actuate the LEDs offset.
• the invention is therefore based on the idea that a single short light pulse from an LED does not leave a visible (toner-developable) effect on the intermediate carrier.
• the combination of several successive light pulses creates exactly the kind of discharge curves that you need for a multilevel operation.
• the shape of the illuminated dot is not important, but only the arrangement, i.e. the sequence of light pulses.
• the resulting discharge curve is generated almost by synthesis.
• Figure 1 is a schematic representation of the components in an electrophotographic printing or copying machine
• FIG. 2 shows a basic illustration of the method
• FIG. 3 shows a discharge curve with a different number of light pulses
• FIG. 4 shows an example of a red dot arrangement for a charge image
• Figure 5 shows the charge image generated on the intermediate carrier for the example of Figure 4;
• FIG. 6 shows a superordinate representation of a control circuit of the exposure device
• Figure 7 is a block diagram of part of the drive circuit
• FIG. 8 is a flowchart according to which the LEDs are controlled.
• FIG. 1 shows a basic illustration of the structure of an electrophotographic printing or copying device in accordance with EP 0 683 954 B1, which is incorporated into the disclosure.
• the following components are arranged around a moving intermediate carrier ZT, in FIG. 1 a photoconductor drum: a charging co-rotron L for charging the intermediate carrier ZT; an LED character generator DK with which the intermediate carrier ZT is reloaded in accordance with the images to be printed and corresponding charge images are generated; a developer station E in which the charge images on the intermediate carrier ZT are colored with toner; a transfer printing station UDS which transfers the toner images from the intermediate carrier ZT to a recording medium AT, e.g.
• the recording medium AT is fed to a fixing station FX after the transfer printing in order to fix the toner images on the recording medium AT.
• the flash of light emitted by an LED is referred to as light pulse LI, the period in which the light pulse is emitted, with light phase LP and the light pulse impinging on the intermediate carrier, which is guided by known optics (EP 0683 954 B1), as light point LE ,
• FIG. 2 shows in principle the course of the method.
• the area to be printed is subdivided into raster cells RZ, which are arranged in rows ZE and columns SA, an LED being assigned to a raster cell of each row.
• the illuminated point LE produced on the intermediate carrier is larger than the line width ZB of a raster cell RZ.
• the comb with the LEDs is arranged in a fixed manner while the intermediate carrier moves past the LEDs.
• Raster cells RZ of the exposure of an intermediate carrier are shown, in line Z2 the number of light pulses LI required for this, in line Z3 the course of the discharge curve LK (the course of the voltage U when the intermediate carrier moves past the LEDs is plotted on the intermediate carrier), which are generated by the light pulses LI.
• the first line ZI shows raster cells RZ which are assigned to an LED.
• the raster cells RZ are broken down, for example, into eight lighting phases LP with the same spacing.
• the second raster cell RZ2 shows an exposure of 25% (ie two light phases) of the raster cell.
• the third raster cell RZ3 the case is shown that no exposure takes place.
• Raster cell RZ4 shows the case in which there is an exposure of 37.5% of the raster cell (in three lighting phases) and in raster cell RZ5 the case in which the whole raster cell (in eight lighting phases) is exposed again. From the representation of line ZI it can be seen that partial exposure of a raster cell RZ only ever occurs with a 100% exposed raster cell RZ, the partially exposed raster cells lying directly in front of or behind the 100% exposed raster cell. In this way the discharged enlarged the area beyond a 100% grid cell and thus adjusted the gray value of the area.
• the number and position of the light points LE (shown in principle as a circle) generated by the light pulses LI on the intermediate carrier are shown, which are generated by the LED and which are larger than a grid cell RZ.
• the number of light pulses per grid cell RZ depends on the gray value that is to be generated in the grid cell. Only if the number of immediately successive light pulses LI is such that the discharge of the intermediate carrier caused by them exceeds the development threshold EW (development level in FIG. 1) of the intermediate carrier (line Z3), is there sufficient discharge of the intermediate carrier by one To enable coloring of the intermediate carrier with toner.
• EW development level in FIG. 1
• line Z3 the light phases LP of the light pulses LI are shown. It can be seen that the light pulses LI follow one another immediately. The basis is the case that a maximum of eight light pulses are emitted per line width ZB (raster cell width). Each LED can shine in each of the light phases. If all eight lighting phases are used, 100% exposure is achieved. The energy per light pulse (e.g. in microjoules) can be identical for all LEDs. The LEDs can be compared via current and / or lighting duration within the lighting phase.
• a light pulse from an LED is not sufficient to discharge the intermediate carrier in the example of FIG. 2 up to the development threshold EW.
• Only the sequence of several light pulses LI for example of 5 light pulses, leads to the crossing of the development threshold EW.
• the number and position of the light pulses In order to print gray values, it is not the burning time of an LED that is modulated, but the number and position of the light pulses.
• the shape of the individual light pulse is no longer important. That I can overlap several light pulses LI, there is a resulting discharge curve, which is formed from similar curves. It is important that the shape of the discharge curve remains constant in a lighting phase. This can be achieved by a short bright light pulse LI or a weaker but longer exposure. The printing speed has no influence on the resulting discharge curve.
• FIG. 3 shows these relationships in a basic representation, which shows the discharge curve LK with a different number of light pulses LI (the voltage U is shown when the intermediate carrier moves in the direction X).
• the course of the discharge curve LK1 for one light pulse LI, the discharge curve LK2 for eight light pulses LI, the discharge curve LK3 for 14 light pulses LI, the discharge curve LK4 for 15 light pulses LI and the discharge curve LK5 are shown
• FIG. 4 shows an example of the exposure or discharge of the intermediate carrier in a basic representation.
• the area to be printed is divided into raster cells RZ arranged in rows ZE and columns SA.
• the luminous point LE which a light pulse LI generates on the intermediate carrier, is larger than the raster cell RZ.
• the direction RK of the LED comb and the printing direction X are also given.
• the luminescent phases LP and thus the area of the exposure or the discharge are indicated in percent in the raster cells RZ.
• the position of the light phases LP on the intermediate carrier is also shown.
• the resulting charge image LA on the intermediate carrier can be seen in FIG. 5.
• the other representation corresponds to FIG. 4.
• 256 combinations of driving an LED are possible.
• 16 are useful, for example, provided that the light pulses are always to follow one another immediately.
• an individually standing light pulse LI is never developed, but only light pulses in connection with 100% exposure, as can be seen, for example, from FIG. 2.
• Control data SD which are coded with a width of 4 bits, are then sufficient to control the LEDs.
• control data SD are given, in the right column the assigned lighting phase data LPD, which indicate whether and at what point a grid cell Light pulse should be generated.
• a "0" is entered in the table for the lighting phases LP if the LED should not light up or a "1" if the LED should light up.
• the control data SD contain the gray values to be printed and a position information.
• the control date SD1 indicates that the light pulse is emitted in the first lighting phase of a raster cell.
• the lighting phase data LPD1 contains a "1" only at the first position.
• the control date SD8 indicates that in all lighting phases of a grid cell
• Light pulse is generated (100% exposure).
• all digits of the assigned lighting phase data LPD8 contain a "1". It can also be seen from the table that it emerges from the lighting phase data LPD before the lighting phase data LPD8 and after that whether light pulses LI are generated before 100% exposure or after.
• a lighting phase data LPD1 occurs e.g. only after a lighting phase date LPD8; on the other hand, a light phase data LPD9 occurs e.g. only before the light phase date LPD8.
• FIG. 6 shows a control circuit comprising a controller CT and a character generator ZG.
• the controller CT has a memory SP for the print data of images to be printed, e.g. coded with 8bit / pixel or 150 lines / inch. This print data is entered into the screening table ST
• Control data SD implemented for the individual LEDs of the comb.
• the control data SD are then transmitted from a transmitter TA to the character generator ZG, specifically to the receiver RV.
• the character generator ZG e.g. 12288 LEDs in groups AR of e.g. 128 LEDs each divided.
• Each group AR is assigned an LED control chip LC which controls the LEDs of the group AR from LEDs.
• the control data SD (called DATA) are fed clocked by a clock CL (clock CL) to a data interface (data interface) DI per group AR of LEDs. The control data will be then forwarded to the data interfaces DI of the other groups AR.
• the ' clock CL is regenerated in a regeneration circuit CR (clock recovery).
• the control data assigned to a group AR are selected by an address decoder ADC.
• the control data SD are stored in a data buffer (line buffer) DP. Several rows of raster cells can be stored simultaneously, so that the line required for printing is always stored in the data buffer DP.
• a correction value memory (LED Adjustment Table) KP contains the correction values for comparing the amount of energy per lighting phase and LED.
• controlled by an address control circuit AC the counter data for the LED of the group AR are stored in the data buffer DP and the correction values are addressed in the correction value memory KP.
• a control unit CU controls the sequence of the activation of the LED using a clock signal from the clock circuit TA.
• the control data SD are transferred from the data buffer DP into an assignment circuit (flash decoder) AD, which controls data SD in control values SG corresponding to the assigned lighting phase data LPD (according to
• Table converts. Via a switch SC, the outputs of the correction value memory KP and the assignment circuit AD are applied to the addressed LED via a down counter ZR, which determines the duration of the light pulse LI. The counter output signal is then fed to a driver circuit TR for the LED, which operates the LED.
• the control unit CU coordinates the operation during operation. Depending on the address of the LED that is to emit a light pulse LI, it addresses the data buffer DP and causes the transfer of the control date SD into the assignment circuit AD. This converts the control date according to the lighting phase data LPD into control values SG which are fed to the switch SC.
• the switch SC applies a signal to the counter ZR which is counted back to zero by the clock from the clock circuit TA. From the beginning of the Starting the counter ZR on until the value zero is reached, the LED lights up. The duration of the light pulse is determined by the correction value, the occurrence or non-occurrence of the light pulse by the control value SG.
• the LEDs of a group AR are connected via buses, a bus for the control values, a bus for the addresses and a line for the clock CL.
• the printing process is thus carried out in the following way:
• Printing is started via the Data Interface DI (Data Interface DI> Address Decoder ADC> AdrsCtrl AC> ControlUnit CU).
• ControlUnit The control unit (ControlUnit) CU starts lighting phase LP1.
• the control unit (ControlUnit) CU fetches the control date for the LED1 from the data buffer DP, checks in the assignment circuit (flash decoder) AD whether lighting is active in this phase and generates the control value SG.
• the switch SC links the value with a correction value from the correction value memory (LED adjustment buffer) KP.
• Control Unit causes the control value to be transmitted via the data bus to the counter ZR and from there to the driver circuit TR operating the LED1.
• Control Unit Control Unit
• FIGS. 5, 6, 8 show a time diagram of the activation of the LEDs of a group AR.
• the eight lighting phases LP1 - LP8 for the 128 LEDs of a group AR are shown.
• the LEDs of a group AR are activated one after the other in the individual lighting phases LP and ignited or not ignited depending on the print data.
• This sequence of activating the LEDs of a group AR takes place in all eight lighting phases LP1-LP8. This ensures that only one LED is lit at the same time in a group AR per lighting phase LP.
• ZT intermediate carrier e.g. Photoconductor drum

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Printers Or Recording Devices Using Electromagnetic And Radiation Means (AREA)

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Citations (6)

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• 2001
  • 2001-10-24 DE DE10152389A patent/DE10152389C2/de not_active Expired - Fee Related
• 2002
  • 2002-10-24 JP JP2003539299A patent/JP2005506233A/ja active Pending
  • 2002-10-24 EP EP02782998A patent/EP1442589B1/de not_active Expired - Lifetime
  • 2002-10-24 WO PCT/EP2002/011909 patent/WO2003036937A1/de active IP Right Grant
  • 2002-10-24 US US10/493,674 patent/US7230634B2/en not_active Expired - Fee Related
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